Keiji uchikawa

Tokyo Institute of Technology, Department of Information Processing, Emeritus

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Papers by Keiji uchikawa

Highly Efficient and Accurate Color Calibration for DLP Projector

The Journal of the Institute of Image Information and Television Engineers, 2016

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超短焦点プロジェクタによる映像歪みの画質定量化

The Journal of the Institute of Image Information and Television Engineers, 2016

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Simultaneous and Successive Comparison for Brightness of Colored Lights

JOURNAL OF THE ILLUMINATING ENGINEERING INSTITUTE OF JAPAN, 1984

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Luminosity thresholds of colored surfaces are determined by their heuristic upper-limit luminances in the visual system

We typically have a fairly good idea whether a given object is self-luminous or illuminated, but ... more We typically have a fairly good idea whether a given object is self-luminous or illuminated, but it is not fully understood how we make this judgement. This study aimed to identify determinants of the luminosity threshold, a luminance level at which a surface begins to appear self-luminous. We specifically tested a hypothesis that our visual system knows the maximum luminance level that a surface can reach under the physical constraint that a surface cannot reflect more light than any incident light and applies this prior to determine the luminosity thresholds. Observers were presented with a 2-degree circular test field surrounded by numerous overlapping colored circles and luminosity thresholds were measured as a function of (i) the chromaticity of the test field, (ii) the shape of surrounding color distribution and (iii) the color of the illuminant of the surrounding colors. We found that the luminosity thresholds peaked around the chromaticity of test illuminants and decreased a...

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Explaining #TheShoe based on the optimal color hypothesis: The role of chromaticity vs. luminance distribution in ambiguous image

The image of #theShoe is a derivative image of #theDress which induced vastly different color exp... more The image of #theShoe is a derivative image of #theDress which induced vastly different color experiences across individuals. The majority of people perceive that the shoe has grey leather with turquoise laces, but others report pink leather with white laces. We hypothesized #theShoe presents the problem of color constancy, where different people estimated different illuminants falling onto the shoe. The present study specifically aimed to understand what cues in the shoe image caused the ambiguity based on the optimal color hypothesis: our visual system knows the gamut of surface colors under various illuminants and applies the knowledge for illuminant estimation. The analysis showed that estimated illuminant chromaticity largely changes depending on the assumed intensity of the illuminant. When the illuminant intensity was assumed to be low, a high color temperature was estimated. In contrast, assuming high illuminant intensity led to the estimation of low color temperature. A sim...

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Color constancy based on the geometry of color distribution

A white surface appears white under different lighting environments. This ability is referred to ... more A white surface appears white under different lighting environments. This ability is referred to color constancy. The physical inputs to our visual system are dictated by the interplay between lights and surfaces, and thus for the surface color to be stably perceived, the illuminant influence needs to be discounted. To reveal our strategy to infer the illuminant color, we conducted three psychophysical experiments designed to test optimal color hypothesis: we internalize the physical color gamut under a particular illuminant and apply the prior to estimate the illuminant color. In each experiment, we presented 61 hexagons arranged without spatial gaps, where the surrounding 60 hexagons were set to have a specific shape in their color distribution. We asked participants to adjust the color of a center test field so that it appears a full-white surface placed under a test illuminant. Results and computational modeling suggested that although our proposed model is limited in accounting...

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Effect of Change in Spectral Transmittance of Crystalline Lens with Aging on Color Vision

JOURNAL OF THE ILLUMINATING ENGINEERING INSTITUTE OF JAPAN, 2000

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The shift of white-point according to the change of illuminant and the segregat ion of surface-and apperent-color perception

JOURNAL OF THE ILLUMINATING ENGINEERING INSTITUTE OF JAPAN, 1995

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Effect of surrounding stimulus to simultaneous color constancy

JOURNAL OF THE ILLUMINATING ENGINEERING INSTITUTE OF JAPAN, 1993

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Measurement of spatial blackness induction

JOURNAL OF THE ILLUMINATING ENGINEERING INSTITUTE OF JAPAN, 1991

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Ranges of Animation Skin Color

International Journal of Affective Engineering, 2017

Skin color has been studied for color rendering since 1950s. The studies contained skin color of ... more Skin color has been studied for color rendering since 1950s. The studies contained skin color of photographs and real skin. However, virtual skin color also became important with developing display recently. In this study, animation skin color was dealt with the main theme, although it has never been treated as a subject before. Two-dimensional animation face images, the farthest from real face, were used as stimuli. In experiments, tolerantly-accepted, preferred, more preferred, and the most preferred skin color were investigated by the cascade selection method. In results, the data points of 50% subjects' consistency fitted ellipses for animation skin color. Moreover, representations of skin color appeared different lightness according facial shapes. In addition, preferred skin colors of animation facial images appeared different in properties from real skin colors, portraits and photographic images. Therefore, skin color representation changes depending on the degree of realism with illuminants and shadows.

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Effects of surrounding stimulus properties on color constancy based on luminance balance

Journal of the Optical Society of America. A, Optics, image science, and vision, 2016

The visual system needs to discount the influence of an illuminant to achieve color constancy. Uc... more The visual system needs to discount the influence of an illuminant to achieve color constancy. Uchikawa et al. [J. Opt. Soc. Am. A29, A133 (2012) showed that the luminance-balance change of surfaces in a scene contributes to illuminant estimation; however, its effect was substantially less than the chromaticity change. We conduct three experiments to reinforce the previous findings and investigate possible factors that can influence the effect of luminance balance. Experimental results replicate the previous finding; i.e., luminance balance makes a small, but significant, contribution to illuminant estimation. We find that stimulus dimensionality affects neither the degree of color constancy nor the effect of luminance balance. Unlike chromaticity-based color constancy, chromatic variation does not influence the effect of luminance balance. It is shown that luminance-balance-based estimation of an illuminant performs better for scenes with reddish or bluish surfaces. This suggests t...

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Temporal Integration for Wavelength Change of an Equal-luminance Single Pulse

Journal of Light & Visual Environment, 1989

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Color vision

IEEE SMC'99 Conference Proceedings. 1999 IEEE International Conference on Systems, Man, and Cybernetics (Cat. No.99CH37028)

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Equating colored lights for saturation (A)

Journal of the Optical Society of America

Dynamics of Asymmetric Color Matching

Optical Review, 2000

It is known that the human color constancy is not complete. We conducted asymmetric color matchin... more It is known that the human color constancy is not complete. We conducted asymmetric color matching experiments to clarify a simple question: what was it that the observer matched. Observers made apparentcolor matches between Munsell color chips under D65 illumination and a color chip presented on a CRT. The observers' matches showed incomplete color constancy. We applied relative cone-weight transformation to each observer's results under control condition, so as to equate the unique-white point for each illuminant condition. The result of this simple transformation showed good match to the actual data. Our results suggest what the observer was doing during the asymmetric color matches was picking up apparent-color signal, achieved from the test color chip under D65, and reconstructing it with respect to the unique-white by a simple cone response scaling.

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Visual attention does not independently influence on chromatic and achromatic contrast-discrimination processes

Journal of vision, 2015

When chromatic and/or achromatic discrimination tasks were performed in central and peripheral vi... more When chromatic and/or achromatic discrimination tasks were performed in central and peripheral visual fields in a dual-task paradigm, performance reduction was observed for the peripheral task, and degree of its reduction depended on combination of colors between the central and peripheral stimuli (Uchikawa et al., 2014). On the other hand, when the observer performed a pattern discrimination task using a dual-ring pattern in the central visual field, the color of the central pattern did not affect the peripheral performance (Sato et al., 2014). In the present study the first experiment was repeated using the dual-ring pattern for the central target to confirm that the importance of color combination was due to the central task itself, but not to the central pattern. The results were consistent with the previous experiments and positive to the hypothesis, i.e. those showed that threshold elevation was significantly larger when chromatic and achromatic discrimination tasks were combi...

Chromatic enhancement of colored picture in memory

Analysis of human perception of facial skin radiance by means of image histogram parameters of surface and subsurface reflections from the skin

Skin research and technology : official journal of International Society for Bioengineering and the Skin (ISBS) [and] International Society for Digital Imaging of Skin (ISDIS) [and] International Society for Skin Imaging (ISSI), 2012

The appearance of the skin is the result of complicated light-skin interactions involving surface... more The appearance of the skin is the result of complicated light-skin interactions involving surface and subsurface reflections. Radiant skin is a complicated attribute but is important for skin beauty. The aim of the present study was to achieve an understanding of the association between human perceptions of skin radiance and image histogram parameters from technically recorded images of surface and subsurface reflections. Facial images of 45 subjects were evaluated visually by 30 respondents and were also computer analyzed in terms of their image histogram parameters. A partial least squares regression model was created to explain visual perceptions in terms of the image histogram parameters. Visual perceptions of subsurface reflections can be explained in terms of the mean from the subsurface reflection image histogram, and visual perceptions of surface reflections can be explained in terms of the standard deviation (SD) and skewness from the surface reflection image histogram. Ski...

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Learning to Recognize Patterns: Changes in the Visual Field with Familiarity

Optical Review, 1995

Two studies were conducted to investigate changes which take place in the visual information proc... more Two studies were conducted to investigate changes which take place in the visual information processing of novel stimuli as they become familiar. Japanese writing characters (Hiragana and Kanji) which were unfamiliar to two native English speaking subjects were presented using a moving window technique to restrict their visual fields. Study time for visual recognition was recorded across repeated sessions, and with varying visual field restrictions. The critical visual field was defined as the size of the visual field beyond which further increases did not improve the speed of recognition performance. In the first study, when the Hiragana patterns were novel, subjects needed to see about half of the entire pattern simultaneously to maintain optimal performance. However, the critical visual field size decreased as familiarity with the patterns increased. These results were replicated in the second study with more complex Kanji characters. In addition, the critical field size decreased as pattern complexity decreased. We propose a three component model of pattern perception. In the first stage a representation of the stimulus must be constructed by the subject, and restricting of the visual field interferes dramatically with this component when stimuli are unfamiliar. With increased familiarity, subjects become able to reconstruct a previous representation from very small, unique segments of the pattern, analogous to the informativeness areas hypothesized by Loftus and Mackworth [J. Exp. PsychoL, 4 (1978) 565].

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Highly Efficient and Accurate Color Calibration for DLP Projector

The Journal of the Institute of Image Information and Television Engineers, 2016

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超短焦点プロジェクタによる映像歪みの画質定量化

The Journal of the Institute of Image Information and Television Engineers, 2016

Download

Simultaneous and Successive Comparison for Brightness of Colored Lights

JOURNAL OF THE ILLUMINATING ENGINEERING INSTITUTE OF JAPAN, 1984

Download

Luminosity thresholds of colored surfaces are determined by their heuristic upper-limit luminances in the visual system

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